Using hCG Levels to Diagnose Miscarriage

Your doctor may use your blood hCG levels to diagnose whether you're having a miscarriage. What exactly do the numbers of this blood test mean, and what does it mean if serial measurements are falling or if they fail to double? What may other tests be done?

What Is HCG?

Human chorionic gonadotropin (hCG) is a hormone produced by the placenta during pregnancy, and an hCG blood test measures the level of this hormone in your bloodstream. There are two different types of hCG blood tests:

  • Qualitative: This type returns a yes/no answer about whether there is hCG in the blood.
  • Quantitative: This type returns a measurement of the precise amount of hCG in the blood.

Why Doctors Order hCG Blood Tests

Some doctors test hCG levels in early pregnancy as a routine part of prenatal care for all women. Most often, however, urine-based hCG tests are used to confirm a pregnancy.

Physicians usually order a quantitative hCG blood test only when they need more information about what is going on in a particular patient’s pregnancy. This may occur if a woman has vaginal bleeding, miscarriage symptoms, a history of or pain that could indicate an ectopic pregnancy.

  • An hCG blood test does not require any special preparation or planning.
  • You do not have to fast before having your blood drawn.
  • The results should not be affected by the time of day you get your blood was drawn.
  • The results are not affected by the amount of water you drink before the test—unlike an hCG urine test, which is affected by the concentration of your urine.

In addition to monitoring your hCG levels, your doctor may also perform an ultrasound, both to help determine if you may have had a miscarriage and to make sure you don't have an ectopic pregnancy.

Serial hCG Blood Tests

A single hCG test may be done to see if your levels are in the normal range of hCG for a specific point in pregnancy. Serial hCG measurements are done to look at hCG doubling times, which gives your doctor an idea of whether or not your pregnancy is progressing as it should.

With serial hCG measurements, quantitative hCG blood tests are drawn two to three days apart. This is because ordinarily, in early pregnancy, the hCG level in your blood doubles every two to three days.

If your hCG doubling time is slower than expected, or if it decreases over time, this may be a sign of a miscarriage or an ectopic pregnancy.

Keep in mind that in roughly 15% of pregnancies, the hCG doubling time is slower than expected, and an abnormally slow increase does not necessarily mean there is a problem with your pregnancy.

When Do hCG Levels Stop Doubling?

It's important to note that hCG doubling time can be an important tool in early pregnancy. However, doubling time slows down as the pregnancy progresses.

By six to seven weeks gestation (or when your level passes 1,200 mIU/ml) doubling time decreases to roughly every three days, and after the level reaches around 6,000 mIU/ml, doubling time occurs every four days. By the time you reach eight to 11 weeks, your hCG level will have reached its peak.

While hCG doubling times become less reliable later in the first trimester, other tools such as transvaginal ultrasound become more important in determining the status of your pregnancy.

When Levels Suggest a Miscarriage

Your doctor is the best person to tell you what your hCG levels mean, because normal hCG levels vary significantly from person to person, and single hCG levels (even single low hCG levels) do not give much information on how a pregnancy is progressing.

In order to make a diagnosis:

  • Your doctor can compare the information from your hCG results to other information in your medical history.
  • Check whether or not you are having miscarriage symptoms.
  • Look at the results of an early ultrasound.

In general, however, if the hCG levels are dropping in the first trimester, this probably is a sign of impending miscarriage. On the other hand, slow-rising hCG levels that do not double every two or three days in early pregnancy may be a sign of problems, but can also occur in a normal pregnancy.

Finally, it's important to understand that hCG levels may persist for up to a few weeks after a miscarriage. In other words, you may continue to have a positive urine or quantitative hCG level even after a miscarriage has occurred.

When Levels Suggest Ectopic Pregnancy

Slow-rising quantitative hCG levels, at least in early pregnancy, may be a sign of an ectopic pregnancy. Since a ruptured ectopic pregnancy can be dangerous, your doctor may recommend a transvaginal ultrasound to look for signs of an ectopic pregnancy.

If your hCG level is at least 1,500 to 2,000 mIU/ml and a gestational sac is not visualized on early ultrasound, an ectopic pregnancy may be present.

Since women may not have any symptoms prior to rupture, carefully following any recommendations about repeat hCG levels and ultrasound examinations is important. 

A Word From Verywell

Monitoring quantitative hCG levels can provide helpful information to assess whether you are miscarrying or have other pregnancy complications such as an ectopic pregnancy.

Since hCG levels vary from person to person, however, serial levels a few days apart give a better idea of the status of your pregnancy. In addition to your hCG levels, your doctor will use other information like any physical symptoms you are experiencing and the results of an early ultrasound to determine if a miscarriage is occurring. 

While you are having your hCG levels monitored you may be feeling anxious, and this is understandable. In coping with this uncertainty, many women don't know if they should be excited about pregnancy or grieving a miscarriage.

Knowing how difficult this uncertainty can be, it may be helpful to ask your doctor questions and inquire about the next steps, so you play a knowledgeable and proactive role in what is going on with your pregnancy.

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